Scientists demonstrate the influence of sunlight exposure on the incidence of autoimmune diseases

More than 2.5 million people worldwide suffer from Multiple Sclerosis (MS). The triggers of this chronic inflammatory disease are still obscure, but might have to do with light! It has become very clear that people from northern Europe, North-America, and Canada are more often afflicted by this disorder than people who grew up near the equator. If infants move to sunnier pastures, the risk to develop MS adapts to the new surroundings. The question was, if environmental factors (i.e. sun exposure) influence the immune system. It was this question the scientists from the Cells-in-Motion Cluster of Excellence at the Münster University wanted to solve. Their result: moderate sun exposure supports the development of a healthy immune system and helps with protecting the central nervous system from unwanted attacks. This effect has been known from other diseases, Prof. Karin Loser from the University Clinic for Dermatology says: „From the treatment of psoriasis we know that UV light has a beneficial effect on the immune system.“ Whether that is true for other disorders as well, the neurological scientists of the university clinic tried to elucidate in collaboration with the dermatology science department - in an animal model as well as in patients.

Over six weeks nine MS patients went into a special-made „sun chamber“. The radiation was performed every workday. „The results are astounding“, Loser says, „we could find more regulatory T- and dendritic cells than before in the blood and the skin of the patients as soon as after the first appointment.“ Both cell types prevent the immune system from attacking the patient - which is the main problem in MS. The team of scientists could prove in skin biopsies that UV-B radiation triggers a complex process in MS patients: In the skin exposed to UV-B radiation tolerogenic dendritic cells are induced, which subsequently „educate“ regulatory T cells in neighboring lymph nodes.
In parallel, the exact molecular pathways could be elucidated in the animal model: the induced regulatory cells migrate from the skin to the site of inflammation, meaning the blood, the bones, or - in the case of MS - the central nervous system. The cells trigger a protective reaction of the immune system and dampen the damaging immune response. However, this protective effect faded out even more quickly than the tan: If the treatment was paused for even a few days, the blood parameters and immune status worsened immediately - in mice as well as men.

The results show very clearly how the environmental factor „UV light“ influences the development and course of MS. „Apparently, there is an axis between skin and nervous system. UV-B radiation influences the immune tolerance in the nervous system. This influence is short-lived, reversible, and surpasses the mere effects of Vitamin-D by far“, Prof. Heinz Wiendl (director of the department of neurology) summarizes. Right now this treatment is no replacement for traditional therapies, but the results of this study might help in expanding the repertoire of MS treatments in the future.

This study was supported by the DFG and the KKNMS and the project is part of the SFB CRC128 „Multiple Sclerosis“ and the excellence cluster „Cells in Motion“ (CiM).

Publication:
Breuer J, Schwab N, Schneider-Hohendorf T, Marziniak M, Mohan H, Bhatia U, Groß CC, Clausen BE, Weishaupt C, Luger TA, Meuth SG, Loser K, Wiendl H. UVB light attenuates the systemic immune response in CNS autoimmunity. Annals of Neurol. 2014 [Epub 28 Apr 2014]